1. Field of the Invention
The present invention relates to a composition for fiber reinforced polyurethane resin (hereinafter, referred to as "a fiber-reinforced polyurethane composition", which has a quick-curing property of giving a cured product at a temperature in the range of from 40.degree. to 60 .degree. C. for 1 to 3 minutes, and the cured product being superior in impact resistance, heat-resistance, and rigidity.
2. Related Background Art
Consumption of plastics is increasing recently in automotive-parts industry associated with the trend toward the light-weight and the diversification of design of cars. In particular, long-fiber-reinforced plastics having a higher rigidity are increasingly used for structural members and semi-structural members.
Heretofore, unsaturated polyester resins have mainly been used for such purposes. These types of resins are known to be molded effectively by use of sheet molding compounds SMC). These resins, however, require a high temperature and a high pressure in processing, thus requiring a large investment for processing machines. A resin injection process is known in which a liquid unsaturated polyester resin composition is injected into a mold containing a fibrous reinforcing material preliminarily, and after closing the mold, the resin is cured in the mold. In this process, however, the resin comes to be cured slowly, resulting in low productivity. Moreover, such types of resins exhibit generally low impact strengths.
On the other hand, polyurethane resins, which are known to give impact-resistant cured products, do not generally have satisfactory heat-resistance. In a method for improving the heat-resistance, a multi-functional polyol is employed to raise crosslinking density in the resin. Although this method accelerates the gellation, it involves problems such that the reaction ratio is low at the time immediately after curing, the unreacted isocyanate groups and hydroxyl groups are liable to remain, thus, the development of the properties is slow, and the properties for practical use is not attained until after several days.
The use of conventional urethanation catalyst for raising reactivity causes premature increase of the liquid viscosity, leading to curing without sufficient penetration of the polyurethane composition into the long-fiber mat. On the other hand, adjustment of the reactivity to allow the polyurethane composition to penetrate into the long fiber mat involves problems that the property development upon curing is poor, and long time is required before the mold removal, thus resulting in low productivity.